Apparatus and method for monitoring and controlling a disc refiner gap

Abstract

An apparatus and method for dynamically monitoring the gap between the refining surfaces of first and second relatively rotating metallic refining members. At least one of the refining members is mounted to a first rotatable shaft which is supported in a housing by lubricated bearing means. When the refining members are in rotating relation, an electrical impedance exists across the gap. The value of the impedance is dependent on the size of the gap. An alternating electrical current is passed through the gap and the voltage across the gap is monitored to provide an indication of the size of the gap. The voltage across the gap can also be used as one input to a circuit which controls the size of the gap by driving an electro/hydraulic system.

I claim: 
     
       1. In a refining apparatus including first and second counter-rotating electrically conductive refining members with spaced refining surfaces facing one another to form a gap in which material can be refined, and means for rotating said first and second members, respectively, on first and second electrically conductive shafts supported in a housing by lubricated bearing means, the improvement comprising: oscillator means for producing a stable high frequency alternating signal;   first means for coupling said alternating signal to one of said first or second shafts;   second means for coupling the other one of said shafts to a return circuit path to provide a complete circuit for said alternating signal across the electrical impedance of said gap; and   means coupled to said circuit for monitoring the size of said gap in accordance with the effects of the electrical impedance of said gap upon said signal.   
     
     
       2. The system of claim 1 wherein said signal is an electric current which produces a voltage across said gap, the magnitude of said voltage being representative of the size of said gap. 
     
     
       3. The system of claim 1 wherein said signal is an electric voltage which produces a current through said gap, the magnitude of said current being representative of the size of said gap. 
     
     
       4. The system of claim 2 wherein said monitoring means is responsive to the magnitude of said voltage. 
     
     
       5. The system of claim 3 wherein said monitoring means is responsive to the magnitude of said current. 
     
     
       6. The system of claim 1 wherein said housing is electrically conductive and said lubricated bearing means, when in motion, provide, for low voltage potentials, a high resistance between said housing and said first and second shafts. 
     
     
       7. The system of claim 6 wherein said second means for coupling comprises an electrical brush having a film of insulating oil on the surface thereof, said oil being in communication with said second rotatable shaft, whereby said brush is capacitively coupled to said second rotatable shaft. 
     
     
       8. The system of claim 1 or 7 wherein said first means for coupling comprises a first electrical brush having a first film of insulating oil on the surface thereof, said first film of oil being in communication with said first rotatable shaft, whereby said first electrical brush is capacitively coupled to said first rotatable shaft. 
     
     
       9. The system of claim 6 wherein said second means for coupling comprises an electrically conductive member spaced from and forming a capacitor in conjunction with said second rotatable shaft. 
     
     
       10. The system of claim 1 or 9 wherein said first means for coupling comprises an electrically conductive member spaced from and forming a capacitor in conjunction with said first rotatable shaft. 
     
     
       11. The system of claim 6 wherein said second means for coupling comprises an electrical brush in communication with said second rotatable shaft. 
     
     
       12. The system of claim 1 or 8 wherein said first means for coupling comprises an electrical brush in communication with said first rotatable shaft. 
     
     
       13. The system of claim 11 further comprising switch means connected to said electrical brush for verifying proper communication between said electrical brush and said second rotatable shaft. 
     
     
       14. The system of claim 1 further comprising electrically actuated means for adjusting the size of said gap, and control means coupled between said monitoring means and said electronically actuated means for driving the latter to maintain said gap at a constant value. 
     
     
       15. The system of claim 14 wherein said control means comprises comparator means having a first input terminal coupled to said monitoring means, a second input terminal adapted to receive a reference signal thereon, and an output terminal coupled to provide a drive signal to said electrically actuated means. 
     
     
       16. The system of claim 15 wherein said electrically actuated means comprises a hydraulic pump controlled by an electric motor coupled to said output terminal of the comparator means, said pump being coupled through hydraulic means to said first rotatable shaft for moving said shaft longitudinally along its axis. 
     
     
       17. The system of claim 16 wherein said hydraulic means comprises a bidirectional piston controlled hydraulic actuator. 
     
     
       18. The system of claim 15 wherein said reference signal dictates the size to which said gap will be adjusted, said system further comprising indicator means responsive to said reference signal for providing an indication of the gap size dictated by said reference signal. 
     
     
       19. The system of claim 1 wherein said monitoring means comprises: amplifier means having an input and an output, said input being coupled to the alternating signal;   rectifier means coupled to the output of said amplifier means for rectifying the amplifier alternating signal;   first comparator means for comparing the rectified signal to a reference signal and producing an output in accordance therewith; and   indicator means responsive to the output of said first comparator means for providing an indication of said gap size.   
     
     
       20. The system of claim 19 further comprising electrically actuated means for adjusting the size of said gap, and control means coupled between the output of said first comparator means and said electrically actuated means for driving the latter to maintain said gap at a constant value. 
     
     
       21. The system of claim 20 wherein said control means comprises second comparator means for comparing the output of said first comparator means to a second reference signal and producing an output adapted to drive said electrically actuated means. 
     
     
       22. The system of claim 21 wherein said electrically actuated means comprises a hydraulic pump controlled by an electric motor coupled to the output of said second comparator means, said pump being coupled through hydraulic means to said first rotatable shaft for moving said shaft longitudinally along its axis. 
     
     
       23. The system of claim 1 further comprising means for calibrating said monitoring means by adjusting the amplitude of said alternating signal. 
     
     
       24. The system of claim 1 wherein said first means for coupling comprises an electrical brush in communication with said first rotatable shaft and further comprising switch means connected to said electrical brush for verifying proper communication between said electrical brush and said first rotatable shaft. 
     
     
       25. The system of claim 1 further comprising switch means for simulating an electrical short circuit across said gap to be used in calibrating said monitoring means. 
     
     
       26. A refining apparatus comprising first and second relatively rotating metallic refining members, said first member being mounted to a rotatable shaft supported in a housing by lubricated bearing means, and said second member having a refining surface spaced from that of said first member to form a gap having an electrical impedance thereacross when said members are in rotating relation, the value of said impedance dependent on the size of said gap, oscillator means for producing a stable high frequency alternating signal;   an electrical brush coupled to said oscillator means and having a film of insulating oil on the surface thereof in communication with said rotatable shaft for capacitively coupling the signal from said oscillator to said first member through said rotatable shaft;   means for coupling to said second member to complete, in series with said gap, a circuit path for said signal; and   means coupled to said circuit path for monitoring the size of said gap in accordance with the effects of the impedance of said gap upon said signal.   
     
     
       27. A method for dynamically monitoring the gap between the refining surfaces of first and second relatively rotating metallic refining members, said first and second members being mounted to first and second rotatable shafts respectively, said shafts being supported in an electrically conductive housing by lubricated bearing means, said method comprising the steps of: rotating said first and second members in opposite directions;   applying a stable high frequency alternating electric current to said first rotating member, said current being electrically isolated from said housing by the high resistance provided by the lubricated bearing supporting said first rotatable shaft;   providing a series return path for said current across said gap to said second rotating member and through said second rotating shaft; and   monitoring the voltage across said gap to provide an indication of the size of said gap.   
     
     
       28. The method of claim 27 further comprising the steps of: comparing a signal derived from the voltage across said gap to a reference voltage to produce a difference signal; and   dynamically controlling the size of said gap by applying said difference signal to electro-hydraulic means for moving one of said rotatable shafts along its longitudinal axis.   
     
     
       29. The method of claim 28 further comprising the step of setting said reference voltage to a predetermined value to maintain said gap at a desired size.